BZOJ 1061 志愿者招募

 1 #include<cstdio>
 2 #include<cmath>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<iostream>
 6 #define inf 0x7fffffff
 7 int tot,go[200005],next[200005],first[200005],flow[200005],cost[200005];
 8 int op[200005],a[200005];
 9 int c[200005],vis[200005],dis[200005];
10 int S,T,n,m,edge[200005],from[200005],ans;
11 int read(){
12     int t=0,f=1;char ch=getchar();
13     while (ch<‘0‘||ch>‘9‘) {if (ch==‘-‘) f=-1;ch=getchar();}
14     while (‘0‘<=ch&&ch<=‘9‘) {t=t*10+ch-‘0‘;ch=getchar();}
15     return t*f;
16 }
17 void insert(int x,int y,int z,int l){
18     tot++;
19     go[tot]=y;
20     next[tot]=first[x];
21     first[x]=tot;
22     flow[tot]=z;
23     cost[tot]=l;
24 }
25 void add(int x,int y,int z,int l){
26     insert(x,y,z,l);op[tot]=tot+1;
27     insert(y,x,0,-l);op[tot]=tot-1;
28 }
29 bool spfa(){
30     for (int i=S;i<=T;i++) vis[i]=0,dis[i]=0x7fffffff;
31     int h=1,t=1;vis[S]=1;dis[S]=0;
32     while (h<=t){
33         int now=c[h++];
34         for (int i=first[now];i;i=next[i]){
35               int pur=go[i];
36               if (flow[i]&&dis[pur]>dis[now]+cost[i]){
37                  edge[pur]=i;
38                  from[pur]=now;
39                  dis[pur]=dis[now]+cost[i];
40                  if (vis[pur]) continue;
41                  vis[pur]=1;
42                  c[++t]=pur;
43                 }
44         }
45         vis[now]=0;
46     }
47     return dis[T]!=0x7fffffff;
48 }
49 void updata(){
50     int mn=0x7fffffff;
51     for (int i=T;i!=S;i=from[i]){
52        mn=std::min(mn,flow[edge[i]]);
53     }
54     for (int i=T;i!=S;i=from[i]){
55       ans+=mn*cost[edge[i]];
56       flow[edge[i]]-=mn;
57       flow[op[edge[i]]]+=mn;
58     }
59 }
60 int main(){
61     n=read();m=read();
62     S=0;T=n+2;
63     for (int i=1;i<=n;i++) a[i]=read();
64     for (int i=1;i<=m;i++){
65          int u=read(),v=read(),c=read();
66          add(u,v+1,inf,c);
67     }    
68     for (int i=1;i<=n+1;i++){
69          int tmp=a[i]-a[i-1];
70          if (tmp>=0) add(S,i,tmp,0);
71          else add(i,T,-tmp,0);
72          if (i>1) add(i,i-1,inf,0);
73     }
74     while (spfa()) updata();
75     printf("%d\n",ans);
76 }